Water vapor is a primary by-product in a Fischer-Tropsch (FT) reaction and its presence is generally detrimental to the overall efficiency of the FT reaction. In a FT reaction, a synthetic gas mixture of carbon monoxide (CO) and hydrogen gas (H2), referred to hereinafter as “syngas”, is converted in the presence of a FT catalyst into hydrocarbon products, water vapor and other byproducts. The syngas may be generated from a number of carbon containing sources such as natural gas, coal (fossil), or bio-mass (renewable). It is often desirable to convert these carbon sources into a liquid hydrocarbon form from their original gas or solid states. There are two major types of catalysts used to catalyze this reaction: iron (Fe)-based catalysts and cobalt (Co)-based catalysts. The FT reaction is a relatively high temperature catalytic reaction. Accordingly, the water produced is generally in the form of water vapor.
Due to the adverse effects of water on this reaction, conventional FT reactors have a relative low rate of per-pass CO conversion. Conventional FT reactors separate water from other reaction products and un-reacted CO and H2 gas after they exit the reactor's outlet. The un-reacted CO is often recycled back to a FT reactor inlet so that it may again potentially be converted into a hydrocarbon.
Efforts with respect to in-situ dehydration in F-T conversion of syngas to hydrocarbon products and water has described in several references. A first example is Espinoza et al., U.S. Pat. No. 6,403,660, which describes the use of slurry and fluidize beds to produce F-T hydrocarbon products. In the case of a slurry bed, a membrane apparatus is disposed within the liquid slurry and is used to remove water from the slurry. In another embodiment, a fluidized bed is used with a membrane apparatus again being disposed in a bed of catalyst. This membrane removes water from the bed during the production of F-T products and accompanying water. However, slurry and fluidized beds have shortcomings relative to using fixed bed reactors.
Rohde et al. proposed a fixed bed reactor with silica membrane or a Ceramic Supported Polymer (CSP) membrane with iron catalyst. For example, see M. P. Rohde, et al., “Membrane Application in Fischer-Tropsch Synthesis Reactor—Overview of Concept,” Catalysis Today 106 (2005) 143-148; and D. Unruh, et al., “In-situ Removal of H2O During Fischer-Tropsch Synthesis—A Modeling Study,” and DGMK-Conference, “Chances For Innovative Processes at The Interface Between Refining and Pertochemistry,” Berlin, 2002, Germany. However, these references fail to address heat management in terms of using commercial viable methods. Also, the use of membranes is not optimized to perform water separation where most produced water has been accumulated.
There is a need for improved designs for reactors in which water is removed in-situ during reactions in which the presence of produced water is detrimental and wherein heat management issues and water removal are also addressed as well as efficient distribution and use of membrane materials.